1. Field of the Invention
The present invention relates to the allocation of a Logical Unit (LU) from inside a storage system to a logical volume inside a storage controller.
2. Description of the Related Art
A storage system comprising a virtual logical storage device by which real capacity is dynamically expanded has been known for some time (for example, Japanese Patent Laid-open No. 2007-310861). In accordance with this kind of technology, when a write is generated to a virtual area, of a plurality of virtual areas comprising a virtual logical storage device, for which a real area has not been allocated, a non-allocated real area from among a plurality of real areas is allocated to this virtual area, and the write-targeted data is written to this real area.
In order from the higher level to the lower level, the storage hierarchy inside a storage system in general constitutes an LU, a logical storage device, and a physical storage device. As one kind of logical storage device, there is the above-mentioned virtual logical storage device. For example, when a write request specifying an LU is received by the storage system, if a virtual logical storage device has been allocated to the specified LU, a write is generated to this virtual logical storage device.
The LU is allocated to a logical volume managed by a storage controller. The storage controller, for example, can be a NAS (Network Attached Storage). The NAS provides the logical volume (specifically, a file system space corresponding to the logical volume), to which the LU (Logical Unit) provided by the storage system has been allocated, to a client.
The types of LU vary depending on the type of physical storage device that constitutes the basis of the allocated logical storage device (for example, a hard disk drive (HDD) or flash memory drive), and different storage modes (in other words, the type of logical storage device that has been allocated, for example, the above-mentioned virtual logical storage device or an ordinary logical storage device). The type of LU allocated to a logical volume will impact the response speed at access and the utilization efficiency of the storage resource. Therefore, it is preferable that the characteristics of the type of LU allocated to the logical volume conform to the characteristics related to an access from a client to this logical volume (for example, the type of file to be accessed, whether read accesses or write accesses are more numerous, and so forth).
However, at the time a logical volume is created, the access characteristics relative to this logical volume are unknown, and therefore, there is no way of knowing what type of LU should be allocated to the logical volume. Therefore, for example, there are times when the type of LU allocated to the logical volume does not conform to the actual access characteristics for this logical volume. A case like this is troublesome in that there is no option other than to continue using the type of LU that does not conform to the access characteristics for the logical volume.